Numerical study on the hydrodynamics of thunniform bio-inspired swimming under self-propulsion

Abstract

Numerical simulations are employed to study the hydrodynamics of self-propelled thunniform swimming. The swimmer is modeled as a tuna-like flexible body undulating with kinematics of thunniform type. The wake evolution follows the vortex structures arranged nearly vertical to the forward direction, vortex dipole formation resulting in the propulsion motion, and finally a reverse Kármán vortex street. We also carry out a systematic parametric study of various aspects of the fluid dynamics behind the freely swimming behavior, including the swimming speed, hydrodynamic forces, power requirement and wake vortices. The present results show that the fin thrust as well as swimming velocity is an increasing function of both tail undulating amplitude Ap and oscillating amplitude of the caudal fin θm. Whereas change on the propulsive performance with Ap is associated with the strength of wake vortices and the area of suction region on the fin, the swimming performance improves with θm due to the favorable tilting of the fin that make the pressure difference force more oriented toward the thrust direction. Moreover, the energy loss in the transverse direction and the power requirement increase with Ap but decrease with θm, and this indicates that for achieving a desired swimming speed increasing θm seems more efficiently than increasing Ap. Furthermore, we have compared the current simulations with the published experimental studies on undulatory swimming. Comparisons show that our work tackles the flow regime of natural thunniform swimmers and follows the principal scaling law of undulatory locomotion reported. Finally, this study enables a detailed quantitative analysis, which is difficult to obtain by experiments, of the force production of the thunniform mode as well as its connection to the self-propelled swimming kinematics and vortex wake structure. The current findings help provide insights into the swimming performance and mechanisms of self-propelled thunniform locomotion.

Tuna locomotion: a computational hydrodynamic analysis of finlet function

“…A no-slip boundary condition was applied at the model surface. Previous numerical results of tuna [13,14,23,24] and jackfish [16] swimming and recent experimental flow visualization of robotic tuna models [25,26] both show that the local flow past the posterior bodies of the fishes/model was converging to the posteriorly narrowed bodies. Therefore, the incoming flow U 1 in this paper was set to be parallel to the stroke plane of finlets to mimic the local flow condition of finlets as in tuna swimming.…”

Evolvement rule and hydrodynamic effect of fluid field around fish-like model from starting to cruising

“…Besides, the turbulent kinetic energy and the turbulent dissipation rate both used the first order upwind scheme to speed up the calculation process. In addition, although T/200 has been proven to be suitable (Li, Liu, & Su, 2017), the time step size was set as T/500, with an oscillation period of T = 1/f , to improve the accuracy in this paper, where f is the undulating frequency of the fish-like model.…”

Computational investigation on a self-propelled pufferfish driven by multiple fins

“…This definition, also known as the Froude efficiency (Sfakiotakis et al, 1999), has been widely used in a number of previous self-propelled studies, such as the anguilliform and carangiform fish (Borazjani and Sotiropoulos, 2010), the thunniform fish (Li et al, 2017), as well as some researches on flapping wings (Abbaspour and Ebrahimi, 2015;Zhou et al, 2016).…”